Piezo actuator

ABSTRACT

A piezoelectric actuator has a multilayered structure of piezoelectric layers with inner electrodes interspersed between them and a contacting of the inner electrodes on alternating sides by means of outer electrodes that can supply an electrical voltage. The respective outer electrodes are attached in a net-like, mesh-like, or screen-like fashion and contacts the respective inner electrodes at least at points in the corner region of the piezoelectric actuator, wherein the outer electrode is guided around the respective corner in a predetermined region extends in the direction of the multilayered structure of piezoelectric layers, and is provided with a terminal there.

PRIOR ART

The invention relates to a piezoelectric actuator, for example foractuating a mechanical component such as a valve or the like, accordingto the features in the preamble to the main claim.

It is generally known that the so-called piezoelectric effect can beused to produce a piezoelectric element comprised of a material with asuitable crystalline structure. When an external electrical voltage isapplied, a mechanical reaction of the piezoelectric element occurs,which produces a pressure or tension in a direction that can bepredetermined as a function of the crystalline structure and the regionsto which the electrical voltage is applied. The structure of thispiezoelectric actuator can be laid out in a number of layers,(multilayered piezoelectric actuators) in which the layers arerespectively interspersed with the electrodes used to apply theelectrical voltage. Such piezoelectric actuators can, for example, beused to operate on/off valves in fuel injection systems of motorvehicles.

A piezoelectric actuator of this kind is known from DE 100 26 005 A1, inwhich the outer electrodes are respectively distributed in a net-like ormesh-like fashion over a side surface and are contacted by therespective inner electrodes at least at points. The net-like ormesh-like outer electrodes extend beyond the multilayered structure ofpiezoelectric layers in such a way that the extensions serve to supplythe electrical voltage via appropriate connections.

ADVANTAGES OF THE INVENTION

The piezoelectric actuator described at the beginning, with outerelectrodes, which are attached in a net-like or mesh-like fashion in theform of so-called screen electrodes and are contacted by the respectiveinner electrodes at least at points, is advantageously modified in thatthe contacting of the inner electrodes is provided in the corner region;the respective net-like or mesh-like outer electrodes are guided aroundthe respective corner in a predetermined region and contact therespective inner electrodes at least in parts.

In a particularly advantageous embodiment, the respective net-like ormesh-like outer electrode extends further in the direction of themultilayered structure of piezoelectric layers and is provided with aterminal there. It is also advantageous in this case for the extensionand the terminal to be disposed in the region of the cross section ofthe piezoelectric actuator, i.e. on the end surface.

According to another embodiment form, the respective net-like ormesh-like outer electrode extends laterally from the piezoelectriclayers and is provided with a terminal there.

In every case, the respective net-like or mesh-like outer electrode canbe advantageously rolled in the region of the extension and thenprovided with the terminal. It is particularly advantageous in this caseif the respective net-like or mesh-like outer electrode and/or theterminal is/are comprised of Invar so that the outer electrode has thesame thermal expansion coefficients as the piezoelectric actuator.

The respective net-like or mesh-like outer electrode and/or terminal canalso be respectively soldered or welded to the inner electrodes.

DRAWINGS

Exemplary embodiments of the piezoelectric actuator according to theinvention will be explained in conjunction with the drawings.

FIG. 1 shows a view of a piezoelectric actuator with a multilayeredstructure comprised of layers of piezoelectric ceramic and a screen-likeouter electrode that extends from the end of the layer structure inorder to produce a contact,

FIG. 2 is a top view of the piezoelectric actuator, with the rolledextensions of the screen-like outer electrode according to FIG. 1, withthe connections for an electrical voltage,

FIG. 3 shows a variant of the rolled extensions of the screen-like outerelectrode, and

FIGS. 4 and 5 each show a detailed view of the outer electrodes that areeither soldered or welded in place.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows a piezoelectric actuator 1, which is comprised in anintrinsically known way of piezoelectric sheets of a ceramic materialwith a suitable crystalline structure so that by making use of theso-called piezoelectric effect, the application of an external electricvoltage to inner electrodes 2 and 3 via corresponding electricalconnections triggers a mechanical reaction of the piezoelectric actuator1. FIG. 1 shows one of the contacts on alternating sides—of the innerelectrodes 2 in this case—in the corner region of the piezoelectricactuator 1, with a net-like, mesh-like, or screen-like outer electrode 4that is guided around the respective corner of the piezoelectricactuator 1 in a predetermined region.

According to FIG. 1, the outer electrode 4 extends with a region 5beyond the end surface of the piezoelectric actuator 1 and is rolled onone side of the piezoelectric actuator 1, thus enabling contact with anelectrical connection 6. FIG. 2 is a top view of this end surface. FIG.3 shows an alternative embodiment of the rolled extension 5 in thecorner region of the piezoelectric actuator 1.

FIG. 4 is a detailed view of how the screen-like outer electrode 4 issoldered or welded to a base metallization 7 and 8 on the sides of thepiezoelectric actuator 1 or, according to FIG. 5, to a basemetallization 9 of the piezoelectric actuator 1 extending along theentire corner region.

1-8. (canceled)
 9. In a piezoelectric actuator including a multilayeredstructure of piezoelectric layers with inner electrodes (2, 3)interspersed between them, a contacting of the inner electrodes (2, 3)on alternating sides with outer electrodes (4) that can supply anelectrical voltage, the respective outer electrode (4) being attached ina net-like, mesh-like, or screen-like fashion and contacting therespective inner electrodes (2, 3) at least at points, the improvementwherein the contacting of the inner electrodes (2, 3) is provided in thecorner region of the piezoelectric actuator (1), and the net-like,mesh-like, or screen-like outer electrode (4) being guided around therespective corner in a predetermined region, and contacting therespective inner electrodes (2, 3) at least in parts.
 10. Thepiezoelectric actuator according to claim 9, wherein the net-like,mesh-like, or screen-like outer electrode (4) includes an extension (5)extending outwardly beyond the multilayered structure of piezoelectriclayers and can be provided with a terminal (6) there.
 11. Thepiezoelectric actuator according to claim 10, wherein the extension (5)and the terminal (6) are disposed in the region of the cross section ofthe piezoelectric actuator (1).
 12. The piezoelectric actuator accordingto claim 9, wherein the respective net-like, mesh-like, or screen-likeouter electrode extends laterally from the piezoelectric layers and isprovided with a terminal there.
 13. The piezoelectric actuator accordingto claim 10, wherein, in the region of the extension (5), the respectivenet-like, mesh-like, or screen-like outer electrode (4) is rolled and isprovided with a terminal (6).
 14. The piezoelectric actuator accordingto claim 11, wherein, in the region of the extension (5), the respectivenet-like, mesh-like, or screen-like outer electrode (4) is rolled and isprovided with a terminal (6).
 15. The piezoelectric actuator accordingto claim 12, wherein, in the region of the extension (5), the respectivenet-like, mesh-like, or screen-like outer electrode (4) is rolled and isprovided with a terminal (6).
 16. The piezoelectric actuator accordingto claim 9, wherein the respective net-like, mesh-like, or screen-likeouter electrode (4) and/or the terminal (6) is/are made of Invar. 17.The piezoelectric actuator according to claim 10, wherein the respectivenet-like, mesh-like, or screen-like outer electrode (4) and/or theterminal (6) is/are made of Invar.
 18. The piezoelectric actuatoraccording to claim 1 1, wherein the respective net-like, mesh-like, orscreen-like outer electrode (4) and/or the terminal (6) is/are made ofInvar.
 19. The piezoelectric actuator according to claim 12, wherein therespective net-like, mesh-like, or screen-like outer electrode (4)and/or the terminal (6) is/are made of Invar.
 20. The piezoelectricactuator according to claim 13, wherein the respective net-like,mesh-like, or screen-like outer electrode (4) and/or the terminal (6)is/are made of Invar.
 21. The piezoelectric actuator according to claim9, wherein the respective net-like, mesh-like, or screen-like outerelectrode (4) and/or the terminal (6) is/are soldered to the respectiveinner electrodes (2, 3).
 22. The piezoelectric actuator according toclaim 10, wherein the respective net-like, mesh-like, or screen-likeouter electrode (4) and/or the terminal (6) is/are soldered to therespective inner electrodes (2, 3).
 23. The piezoelectric actuatoraccording to claim 11, wherein the respective net-like, mesh-like, orscreen-like outer electrode (4) and/or the terminal (6) is/are solderedto the respective inner electrodes (2, 3).
 24. The piezoelectricactuator according to claim 12, wherein the respective net-like,mesh-like, or screen-like outer electrode (4) and/or the terminal (6)is/are soldered to the respective inner electrodes (2, 3).
 25. Thepiezoelectric actuator according to claim 13, wherein the respectivenet-like, mesh-like, or screen-like outer electrode (4) and/or theterminal (6) is/are soldered to the respective inner electrodes (2, 3).26. The piezoelectric actuator according to claim 16, wherein therespective net-like, mesh-like, or screen-like outer electrode (4)and/or the terminal (6) is/are soldered to the respective innerelectrodes (2, 3).
 27. The piezoelectric actuator according to claim 9,wherein the respective net-like, mesh-like, or screen-like outerelectrode (4) and/or the terminal (6) is/are welded to the respectiveinner electrodes (2, 3).